(1) Field of the Invention
The present invention relates generally to optical fibers, fiber optic components and devices and, more particularly, to a hermetically sealed and packaged fiber optic coupler/splitter.
(2) Description of the Prior Art
Over the last 15 years, a number of fiber optic components and devices such as: couplers, attenuators, wavelength division multiplexers/de-multiplexers, connectors, filters, switches, fiber-pigtailed semiconductor lasers, isolators, etc., have been developed for use in fiber optic communication systems, sensors and instrumentation. In nearly all of these applications employing fiber optic components or devices, design specific mounting fixtures are utilized to precisely align, position or secure optical fibers or elements within such optical fiber components or devices. In most of these applications, it is common for such mounting fixtures to be formed of a fused silica material because its low coefficient of thermal expansion closely matches that of the optical fibers and other optical components or devices. In this respect, maintaining the stability and relative position of optical fibers, components or devices, through the correct choice of materials, is particularly critical in that even minor relative movements between such elements may result in large variations or degradation in optical characteristics, such as coupling ratios and insertion losses.
Optical fibers, components and devices are typically secured with epoxy adhesives. Most common types of epoxy adhesives used in these applications cure upon exposure to either UV light or heat. The epoxy adhesives are widely used because they are inexpensive, easy to use, and in many instances readily cured. Rapid in-situ cure schedules are also well suited for volume manufacturing.
While epoxies offer a convenient means for attaching optical fibers, components or devices to substrates or to other optical fibers, components or devices, the physical properties of cured epoxies often make such materials less than ideally suited for use in fiber optic systems. In one respect, epoxies have a tendency to absorb moisture. Such tendency is detrimental in that moisture significantly reduces an epoxy's ability to firmly secure the optical fiber, optical components or devices, or to a substrate. In addition, the cured epoxy swells as it absorbs water vapor, and this swelling may strain the relative attachment between optical fibers, or optical components, or optical devices or to a supporting substrate. In general, moisture induced swelling and subsequent degradation of the epoxy adhesive may cause misalignment or even detachment of the optical fibers, components or devices relative to a supporting substrate or other optical elements.
As fiber optics continue to penetrate the telecommunications market, product lifetimes of 20 years or more will be mandatory. In order to achieve this degree of performance, new packaging techniques and materials will be required for reliably attaching optical fibers, components, or devices to supporting substrates and to each other.
U.S. Pat. No. 5,500,917, issued to Hani et al., discloses a method of bonding glass-based optical elements, comprising the steps of positioning a first glass-based optical element relative to a second glass-based optical element, applying a glass-based bonding compound about the first and second optical elements, and applying sufficient localized heat to the glass-based bonding compound to cause the glass-based bonding compound to soften and fuse with the optical elements.
U.S. Pat. No. 5,285,512, issued to Duncan et al., discloses a hybrid fiber optic transceiver which includes a transmitter for converting electrical data signals to corresponding light energy, a receiver for converting optical data signals back to electrical data signals and a clock recovery mechanism to maintain the electrical data signals outputs from the receiver in their proper order. The transceiver also includes an optical splitter or coupler that allows light signals to be transmitted and received over a single fiber. The opto-electrical hybrid circuitry of the transceiver and the fiber optic coupler are enclosed in a small light weight package which is hermetically sealed.
U.S. Pat. No. 4,931,076, issued to Berkey, a method of making an economical fiber coupler comprises providing a glass tube having first and second end portions and a midregion, and a longitudinal aperture extending therethrough. Two suitably prepared glass optical fibers, each having a core and cladding, are disposed within the longitudinal aperture, the fibers extending beyond each end thereof. The fibers are held taut to effect a tension therein, and they are glued to each end portion. The midregion of the member is heated, collapsed about the fibers, and drawn to reduce the diameter thereof.
Still, there remains a need for a new and improved fiber optic coupler, especially suitable for planar arrays, which is capable of achieving a product lifetime of twenty years or more. This improved coupler must be sufficiently sealed in order to repel moisture and avoid swelling due to the absorption of such moisture.